AC-to-DC converters are used to convert an AC input voltage, such as a fully-rectified AC line voltage from a power outlet, to a regulated DC output voltage at a desired output voltage level. To meet regulatory requirements, AC to DC convertes are designed with power factor correction (PFC) to achieve a high power factor while reducing total harmonic distortion (THD). Various topologies have been proposed for AC-To-DC converters incorporating power factor correction (PFC). For example, a conventional boost topology useds a bridge rectifier (also referred to as a diode bridge) to rectify the AC input voltage to DC followed by a boost converter functioning as an active PFC circuit FIG. 1. The boost converter attempts to maintain a constant DC bus voltage on its output while drawing a current that always in phase with and at the same frequency as the line voltage. However, the boost converter suffers significant power loss due to rectified diode and the boost switch power loss. One method uses a critical boundary boost power factor correction, in this design, the inductor current is allowed to completely go to zero before the next switching cycle of the mosfet is initiated and all diode losses are due to forward conduction. But it is difficult to design a controller with stable operation and fast transient response for both modes, the boost converter will be unstable between DCM and CCM. The present invention overcomes the above problems by using a forward transformer to prevent the rectifier reversed conduction loss and mosfet turn on loss.